A wide variety of piezoelectric devices are in common use in various electronics applications. One common type of piezoelectric device is a crystal resonator. A typical crystal resonator includes a layer of crystalline piezoelectric material having opposite faces, with each face having a corresponding electrode bonded thereto, thereby sandwiching the piezoelectric material between the electrodes. The crystal resonator vibrates in response to an electrical stimulus applied to the electrodes. The vibration induces a highly stable electrical oscillation across the electrodes that is useful for timing other devices. Another common type of piezoelectric device is the crystal filter. One variety of crystal filter includes a layer of crystalline piezoelectric material having opposite faces, an electrode affixed to one of the faces, and a pair of electrodes affixed to the other face. The pair of electrodes induces two frequency peaks in electrical conductivity of the crystal filter, with a bandpass filter being formed by suitably adjusting the location of the peaks.
For a piezoelectric device to operate properly, it is important for its elastic properties to fall within design specifications. For example, if the stiffness of a crystal resonator falls outside design specifications, the crystal resonator may not have the desired oscillation frequency. Similarly, if the stiffness in a crystal filter falls outside design specifications, the crystal filter may not have the desired magnitude response. Unfortunately, it has proven very difficult to provide piezoelectric devices with precisely determined elastic properties. One reason for this difficulty is that there is considerable interplay between the various elastic properties of a piezoelectric device. For example, increasing electrode mass to reduce acceleration sensitivity may yield an undesired side effect such as a shift away from desired resonant frequency.
Due to such difficulties, piezoelectric devices generally are formed in a rough state that is not guaranteed to be within final design specifications. The piezoelectric devices may then be brought into final design specifications by adding or removing material from the piezoelectric device. In one conventional approach, material is added or removed from electrodes. In another conventional approach, stiffening electrical fields are applied to a piezoelectric device during operation. In a third conventional approach, a piezoelectric device is stiffened to reduce acceleration sensitivity by adding one or more braces either on the electrodes or on the layer of piezoelectric material.
Such conventional approaches to providing piezoelectric devices with desired elastic properties are undesirable. They are not truly design based, but rather require extra fabrication steps, such as adding or removing material from electrodes, or special operating environments, such as appropriate stiffening electrical fields. Generation of stiffening electrical fields may require additional circuitry. Conventional approaches typically also require the formation of various prototype devices to determine how to fabricate the piezoelectric device with a suitable rough state as described above. Further, conventional approaches are believed to work poorly where electrode thickness exceeds about two percent of total device thickness.
There is accordingly a continuing need in the electronics arts for an improved system and an improved method for providing piezoelectric devices with desired elastic properties. Such system and method preferably should be designed based, so that extra fabrication steps and generation of special operating environments are avoided. Such system and method preferably should be usable with a wide variety of piezoelectric devices, including crystal filters and crystal resonators. Further, there is also a continuing need for improved piezoelectric devices which meet final design specifications without the need for post production processing of the devices.